Semiconductor fabrication processes are typically conducted with the substrates supported within a chamber under controlled conditions. For many purposes, semiconductor substrates (e.g., wafers) are heated inside the process chamber. For example, substrates can be heated by direct physical contact with an internally heated wafer holder or “chuck.” “Susceptors” are wafer supports used in systems where the wafer and susceptors absorb heat.
Some of the important controlled conditions for processing include, but are not limited to, fluid flow rate into the chamber, temperature of the reaction chamber, temperature of the fluid flowing into the reaction chamber, and wafer position on the susceptor during wafer loading.
Heating within the reaction chamber can occur in a number of ways, including lamp banks or arrays positioned above the substrate surface for directly heating the susceptor or susceptor heaters/pedestal heaters positioned below the susceptor. Traditionally, the pedestal style heater extends into the chamber through a bottom wall and the susceptor is mounted on a top surface of the heater. The heater may include a resistive heating element enclosed within the heater to provide conductive heat and increase the susceptor temperature.
A wafer is generally processed at a temperature significantly above room temperature, thereby requiring a significant heat ramp up and ramp down window. A wafer center position is traditionally found by fitting a unique reactor lid having an opening to see the wafer position. The operator will heat the chamber to some temperature below a processing temperature, usually around 200 degrees C. and perform several load and unload steps to determine where the proper wafer loading point is. Next, the operator will cool the chamber under vacuum and then further cool after backfilling to atmospheric pressures. All of these steps and procedures can take more time than is desired.